Mysql我怎么能从第二个sql两个表和countid计数

Question

我正在尝试创建一个Sql，它从第一个表“posts_main”获取所有数据，然后从第二个表“posts_comments”获取注释计数

我试过了：

$sql = "SELECT * FROM posts_main, count(posts_comments.groupid)
INNER JOIN posts_comments ON posts_comments.groupid = posts_main.id
WHERE posts_main.user_id = '$user_id'
GROUP BY posts_main.id";

拜托，我该怎么做？

谢谢....

Answer 1

尝试使用以下查询。

$sql = "select posts_main.*, 
(select groupid from posts_comments where groupid = posts_main.id group by groupid ) as count_group 
from posts_main 
WHERE posts_main.user_id = '$user_id' ";

Answer 2

尝试使用子查询

SELECT posts.*,cnt FROM posts_main  
INNER JOIN (select posts_comments.groupid,count(posts_comments.groupid) as cnt
group by posts_comments.groupid)a
ON a.groupid = posts_main.id
WHERE posts_main.user_id = '$user_id'